1. Field of the Invention:
This invention relates in general to manufacturing tool holders and in particular to a fixture for holding a drill that allows limited floating movement to assure precise alignment of the drill within a template in robotic applications.
2. Description of the Prior Art:
In aircraft manufacturing, certain parts require numerous precisely positioned holes. To maintain tolerances, a template with guide holes is secured over the workpiece or member to be drilled. In one prior art technique, a self-feeding drill is used. The drill has a tube or sleeve on its end that encloses the bit. The sleeve is dimensioned to fit tightly in the guide hole. The operator manually pushes the sleeve into a guide hole. Once in place, the operator actuates the drill, which simultaneously rotates the bit, and advances it into the workpiece. The sleeve avoids wear of a rotating drill bit against a guide hole. This manual drilling is a time consuming operation.
"Robots" having control arms that move to a selected point in space and perform a function are known, such as those that perform certain welds in automobile assembly. Setting up a robot to drill holes in an aircraft member with very close tolerances and over several feet of space has not been done previously, as far as is known to applicants. One problem is that available robots can position a drill bit at a selected point only within 0.050 inch tolerance, insufficient for this type of drilling. The sleeve would not be able to enter the guide hole, which may have a tolerance of only 0.005 inch.
Floating tool holders, or compliance devices, that provide some flexing to aid in alignment are known in the prior art. For example, a driving connection is shown in U.S. Pat. No. 1,782,633 that allows the cutting tool to move angularly and parallel with respect to its drive member. In this patent, however, and in the other patents known to applicants, the entire compliance mechanism is located in the drive train and thus will rotate with the cutting tool. Using this device with a template system would not provide sufficiently close tolerances because clearances would have to be provided in the template guide holes to accomodate the rotation.